After items have been washed in a washing process of a dishwasher, the items are dried in a drying process. For performing such a drying process, the dishwasher is equipped with a drying system.
A closed drying system is shown in GB 2263969, in which a first fan circulates air in a closed system to and from a wash chamber through a circulation duct. Also, a second fan propels air received from outside the dishwasher via another duct in the dishwasher and further to an exhaust opening back to the outside of the dishwasher. A heat exchanger is located between the two ducts. Thereby, the hot, humid, air from the wash chamber is cooled by the cool air received from the outside, and water is condensed from the humidity of the circulated air and air with less humidity is led back into the wash chamber. Such a closed system has the drawback of having a rather low drying efficiency, resulting in a slow drying process.
In an open system, the drying process is performed by the humid air exiting to the surroundings outside the dishwasher. When humid air, comprising a high degree of water vapour, cools down at objects outside the dishwasher, there may be problems due to condensation at the objects, which may result in damp stains on floors or furniture, and other problems related to moist or damp. Also, if the temperature of the exiting humid air is high, it may be dangerous for a user of the dishwasher, or at least the exiting air may be uncomfortable for the user.
EP 1447042 shows a drying system for dishwashers, which is a mix of an open system and a closed system. The drying system has a fan comprising two stages, a first stage for drawing out humid air from the wash chamber and for returning the humid air to the wash chamber, and a second stage for drawing fresh air and using it for cooling the humid air drawn out from the wash chamber. The humid air of the first stage is circulated in the wash chamber via a channel that passes through a condenser. The condenser is cooled by the fresh air of the second stage. Also, a predetermined amount of humid air can be mixed with the fresh air. Thereby, the system described is a closed system with an exhaust air fraction. The possibility to mix an amount of the humid air with fresh air is used for achieving a more efficient drying process. The exhaust air fraction can be adjusted at design level or by installation to offer flexibility for different installations of the dishwasher. Such a solution has a higher efficiency than a totally closed system, and the exhaust air has a rather low temperature, although, the efficiency will not be as high as in an open system. Another drawback of this solution is that after the dishwasher has been installed the exhaust air fraction will be the same irrespective of whether a drying process has just started or it at its end, and irrespective of possible different selectable drying programs of the dishwasher, which would result in an exhaust air with varying exhaust air temperature and humidity. Therefore, there is still a need to achieve an efficient drying process, without risking that air leaving the dishwasher will give rise to moisture problems in the surroundings of the dishwasher.